iVillage.com: Most Dangerous Exercise Machines at the Gym

Leg Extension Machine (Legs, Quads)

This seated exercise puts all the weight resistance in front of your ankles. As you straighten your legs you push the weight up. "This puts extraordinary stress on your knees," says Ramirez. "If you use too much weight, it can result in a torn meniscus (cartilage) or ACL (one of the four major ligaments of the knee). Safer pick: Campfire squats These work the same muscles without the knee stress. Stand with toes pointed out to 10 and 2 o'clock. Bring elbows between your knees and hands together in a prayer position. Straighten your legs, lift your butt up towards the ceiling, and bring it back down. Repeat 20 times.

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To use this machine, you sit with a straight bar behind your neck with your arms bent in "goal post" formation, as you push the bar up and overhead. "Problem is, when you place your shoulders into this extreme external rotation it stresses the shoulder joint and increases the risk of impingement," says Brad Schoenfeld, author of "Sculpting Her Body Perfect." Impingement occurs when the space between the rotator cuff muscles and a bone on top of the shoulder narrows, pinching the tendons.

Safer Pick: Front Dumbbell or barbell shoulder presses Hold dumbbells out to the sides with your wrists stacked above your elbows at a right angle. Push them overhead and together and then back to the starting position. Repeat 12 to 15 times for two to three sets.

This machine locks hips into position so only your waist moves. This puts you in a very inefficient position and puts a lot of torque on the spine, says Schoenfeld. "It's especially dangerous when initiating the movement -- that’s when there's greatest stress on the spine."

Safer Pick: Wood chops with a medicine ball This move is more effective and less stressful to the spine.

Stand with feet slightly wider than shoulder width apart and extend a light-to-medium medicine ball (5 to 6 pounds) in front of you. Bend knees and hips, dropping into a squat as you bring the ball down to touch your left foot, shin or knee (depending on your flexibility). Rise up out of the squat as you simultaneously rotate and raise the ball up and across your opposite side, as if throwing it over your opposite shoulder. Do 10 lifts to each side for two sets.

This seated exercise requires you to push against resistance as you tip backward, using your lower back (lumbar) muscles. "The spine starts off in an 'off' position and pushing it back only puts more stress on the lumbar spine," says Schoenfeld. Safer pick: Good mornings These strengthen the same muscles and allow you to maintain a neutral spine, says Schoenfeld. Hold a barbell behind the head, near the upper back. Keeping your back straight (very important) and knees slightly bent, bend forward until your torso is nearly parallel to the floor. Slowly return to starting position. Start with a weighted body bar for eight to 10 reps for two sets.

On this machine, you pull a bar down behind your neck, which requires you to rotate your shoulders externally. This produces similar stress to the shoulders as that of the shoulder press, says Schoenfeld. "You also often end up smashing the bar into the back of your neck, which can damage the little bony processes." Safer pick: Lat pull down in front Use the same cable but pull it down to the front, not behind your neck. Anchor yourself in the pull down seat and grasp a bar slightly wider than shoulder width. Lean back slightly and focus on squeezing your shoulder blades together as you pull down the bar to touch just below your collar bone -- this way, you’re still working the back. Slowly allow the bar to return to the starting position. Do not rock back and forth, but keep your torso stable. Repeat 10 to 12 reps for two to three sets.

"It's one of the worst machines because it puts pressure on the knee joint and the entire low back," says Tim Ramirez, D.C., founder of PacificaWellness.com in Costa Mesa, Calif. "Plus, most people put too much weight on it." Safer pick: Stiff-legged deadlifts They activate all the same muscles in the correct sequence with less risk, but they must be performed perfectly, says Ramirez. Stand with arms straight down, weighted body bar in front of your thighs. Engage the abdominals as you bend forward at the hips, keeping back straight and knees slightly bent. Do not round your back! Bend forward only as far as you can without losing your form and then slowly stand back up by pushing your heels into the ground. Repeat 10 to 12 times for two to three sets.

This seated exercise puts all the weight resistance in front of your ankles. As you straighten your legs you push the weight up. "This puts extraordinary stress on your knees," says Ramirez. "If you use too much weight, it can result in a torn meniscus (cartilage) or ACL (one of the four major ligaments of the knee). Safer pick: Campfire squats These work the same muscles without the knee stress. Stand with toes pointed out to 10 and 2 o'clock. Bring elbows between your knees and hands together in a prayer position. Straighten your legs, lift your butt up towards the ceiling, and bring it back down. Repeat 20 times.

When guys ask each other "how much can you bench?" they're referring to this classic bench press. While it targets all the main chest muscles, it's difficult to do properly, says Ramirez. "Because one arm is usually stronger than the other, there's a good chance you're not handling the bar equally on both sides, which puts you at risk for injury." One false move and it lands on your chest or neck. Safer pick: Push-ups Form is key. Keep your back straight (do not allow hips to sag) and make sure your fingers are pointed forward. Aim for 12 to 15 reps for two to three sets.

It's easy to use but it's easy to hurt yourself, says Ramirez. "People usually use too much weight and use just about every muscle except for their abs to bring it forward. They use their neck, back and legs instead of their abs." Fail. Safer pick: Crunches For a real challenge, try crunches on an exercise ball. Just make sure to pick the right size for you. A 55-centimeter ball works best for most women. You should be able to sit on the ball with your legs bent at a right angle, thighs parallel to the floor. Perform as many as you can in good form for two to three sets.

Women believe doing this seated outer thigh machine will tone and tighten their outer thighs, but it's simply not going to happen, says Ramirez. Instead, when you're pushing out you just put pressure on the thigh and hip bones. Not only is it irritating to those bones, it may cause a hernia or symptoms of sciatica (pain and numbness of the leg). Safer pick: Leg lifts with ankle weights Use two-to-five pound ankle weights. Lie on your side with your head resting on your arm, legs stacked straight. Raise the top leg straight up and then back, tracing a capital letter "D" as you bring the leg back down to meet the bottom leg. Without actually resting the leg, lift it back up and to the front. Trace a lowercase letter “r” as you bring it back toward the lower leg. Lift the leg straight up one more time. Slowly lower. Repeat 25 to 50 reps per leg for two sets.

Stretching machines may seem like a relaxing, passive way to get more flexible. But they make it too easy to overstretch, says Ramirez. "The machine does all the work so you can easily strain a muscle or end up with a groin pull." Safer pick: Yoga In yoga, you stretch on the ground or the mat and use only your own body weight to stretch. Take a class and hold each pose for 30 seconds or as your yoga instructor recommends.